Rings around Brush instead of being feathered.

[Jafaraway]

I'm new here. Been using gimp for a long time now and sometimes run into the problem I'm currently having. Sometimes when I use one of the standard feathered edge brushes in a transparent layer, the brush's edges are a bunch of concentric circles, instead of being nice and feathered. However if I use the same brush directly on the background, it does look nice and feathered. Is there a setting that fixes this? Or am I doing something wrong?

See attachment. Thank you to anyone who can help with this.